1. Field of the Invention
The present invention generally relates to the field of inspection and analysis of specimens and, more particularly, to defect localization in semiconductor integrated circuits.
2. Description of Related Art
The metallization and thin film layers of conventional integrated circuits contain interconnects such as vias, contacts, and windows. The interconnects are arranged to allow electrical contact between transistors and other circuitry in an integrate circuit. However, a variety of factors may cause defects in the interconnects. Defective interconnects can ultimately lead to failure of the integrated circuit by causing open circuits.
One type of defect is a void formed in the via. Voids may be caused by a variety factors such as stress, electromigration, and impurities. As line widths continue to decrease in size, even small voids can prevent an integrated circuit from operating properly. Other types of defects are dishing and erosion that can result from processes such as chemical mechanical polishing (CMP) during the damascene and dual damascene processes. Dishing and erosion often results from polishing of the conductive layer to an extent such that insufficient conductive material is available to connect circuit elements.
Inspection of integrated circuit at various stages of manufacture can significantly improve production yield and product reliability. If a defect can be detected early in production, the cause of the defect can be determined and corrected before a significant number of defective IC""s are manufactured.
Conventional defect detection systems frequently use the xe2x80x9cvoltage contrastxe2x80x9d technique. The voltage contrast technique operates on the basis that potential differences in the various locations of a sample under examination cause differences in secondary electron emission intensities when the sample is the target of an electron beam. Thus, the potential state of the scanned area is acquired as a voltage contrast image such that a low potential portion of, for example, a wiring pattern might be displayed as bright (intensity of the secondary electron emission is high) and a high potential portion might be displayed as dark (lower intensity secondary electron emission). Alternatively, the system may be configured such that a low potential portion might be displayed as dark and a high potential portion might be displayed as bright.
A secondary electron detector is used to measure the intensity of the secondary electron emission that originates only at the path swept by the scanning electron beam. A defective portion can be identified from the potential state of the portion under inspection. In one form of inspection, the mismatched portion between the defective voltage contrast image and the defect free one reveals the general defect location.
Other techniques involve slicing a wafer into cross sections and using an electron microscope to detect defects. Intrusive methods, however, are both time consuming and wasteful. Acoustic and optical methods are also available, but can only be used in particular circumstances. For example, optical methods are often only effective in very specific circumstances.
Conventional systems do not allow efficient localization of defects. Accordingly, additional improved detection systems allowing more effective localization of defects are desirable
The present invention includes a system for localization of defects in test samples. A sample is scanned using a particle beam. Some particles interact with conductive elements and may cause the emission of x-rays. Other particles can pass through the sample entirely and generate a current that can be measured. A higher current generated indicates less conductive material at the scan target that may mean a void, dishing, or erosion is present. Localization of a defect can be confirmed using an x-ray emission detector.
An apparatus for localizing a defect in a first scan target associated with a sample having a first surface and a second surface is provided. A particle beam generator is configured to scan a first scan target. The particles interact with a first material in the scan target. A generated current detection system is configured to obtain a measurement of generated current resulting from the scan of the first scan target. The measurement of generated current is compared with a control measurement to provide information for localization of a defect in the first scan target.
A system for localizing a defect in a sample sample having a first surface and a second surface is provided. The system includes a memory and a processor coupled with memory. The processor is configured to identify a first measurement of generated current resulting from a particle beam scan of a first scan target and a second measurement of x-ray emissions from the first surface. The processor is further configured to identify a control measurement and provide the first measurement and the control measurement for comparison to thereby provide information for localizing a defect associated with the first scan target in the sample.
According to still another embodiment, a method for localizing a defect in a sample is provided. A first measurement of generated current resulting from a particle beam scan of a first scan target is provided. A control measurement is provided. The first measurement and the control measurement are provided for comparison to thereby obtain a characterization of a defect associated with the first scan target in the sample.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example various principles of the invention.